Young homosexual men have not been reached by existing AIDS prevention campaigns. Whereas most older gay men in urban areas have stopped engaging in sexual behaviors that can transmit HIV infection, high numbers of young homosexual men continue to engage in activities that place them and others at risk for contracting HIV. AIDS prevention programs tailored specifically to the unique needs and subculture of young homosexual men are urgently needed. Community-level preventive interventions, which have been proven effective in promoting a variety of health behaviors, have been advocated as effective and feasible for halting the AIDS epidemic. Peers are theorized to be especially influential in behavior change with young homosexual men. We propose to implement a peer-led community-level intervention program sequentially in three medium-sized West Coast cities to assist young homosexual men (aged 18-25) to: a) reduce the frequency with which they engage in high risk sexual activities, and b) influence variables theorized to be related to risk-reduction, according to our theory, the AIDS Risk Reduction Model. Pilot data in these communities indicate that 40% of the young men had engaged in unprotected intercourse in the prior six months. A multiple baseline design using longitudinal data will be used to evaluate the efficacy of the intervention. We will examine short-term (immediately afterwards and six months afterwards) and long-term (one year) effects of the program. Cross-sectional samples to check for biases in the longitudinal sample will also be collected. Guided by our previous research using the AIDS Risk Reduction Model, the proposed intervention targets critical variables that must be changed to promote HIV risk-reduction for young homosexual men. Diffusion theory underlies the intervention design, which is a community mobilization strategy to promote norms for safer-sex among young homosexual men. The mobilization strategy will include three central elements: 1) a system of peer outreach by which young homosexual men will become involved in communicating the need for safer sex to their peers in formal and informal settings, 2) a series of peer-led HIV risk-reduction workshops for young homosexual men to discuss and overcome barriers to safer sex, and 3) an ongoing publicity campaign about the intervention program within the gay community that established an awareness and legitimacy of intervention activities among young homosexual men and provides a continual reminder of the norm for safer sex. Through this approach of mobilizing the communities we hope to reach all young men who have sex with men, regardless of their sexual identification or whether they are willing to attend the structured intervention activities. If successful, the intervention an feasibly be adopted in communities outside of major gay metropolitan areas.